In the communications field, an ingress port of a switching device receives a data packet and splits the data packet into multiple cells, and the cells pass, inside the switching device, through multiple switching units, and reach an egress port of the switching device along different paths. The egress port sequences the multiple cells, and then sends the multiple cells.
FIG. 1 shows a switching structure inside one switching device, where a fabric interface chip (Fabric Interface Chip, FIC for short) and a sending port S1/3 are located in a same line card chassis (Line Card Chassis, LCC for short), and a sending port S2 is located in a fabric card chassis (Fabric Card Chassis, FCC for short). The sending port S1/3 includes a sending port S1 and a sending port S3, and S1/3 is connected to the FIC through S1, and S1/3 is connected to S2 through S3. If the FIC receives a data packet sent by another switching device and splits the data packet into multiple cells, the cells are forwarded from the FIC to S2 through S1/3, and then forwarded to a destination S1/3 through S2, the destination S1/3 forwards the cells to a destination FIC, and finally the destination FIC sends the cells to another switching device.
FIG. 2 shows a format diagram of a cell frame, where the first field in the cell frame is a timestamp TS, which indicates a timestamp of a time when an FIC sends the cell. S1, S2, and S3 forward the cells according to TS values, where a cell whose TS value is smaller is forwarded first and a cell whose TS value is larger is forwarded later. For example, an FIC in an LCC A and an FIC in an LCC B send cells C1 and C2 at a same time T1 respectively, where C1 and C2 carry a same timestamp T1. Before C1 and C2 enter an optical fiber link L1 and an optical fiber link L2 respectively, both L1 and L2 bear cells whose timestamps are less than T1. If L1 is longer than L2, cells that are borne in L1 and whose timestamps are less than T1 are more than cells that are borne in L2 and whose timestamps are less than T1, and C2 reaches S2 earlier than C1 does. Because S2 forwards a cell whose TS value is smaller first, and forwards a cell a cell whose TS value is larger later, after C2 reaches S2, C2 can be forwarded only after S2 completes forwarding the cells that are borne in L1 and whose timestamps are less than T1, that is, C2 can be forwarded by S2 only after C1 has reached S2. If L1 is much longer than L2, C2 needs to wait a quite long time before being forwarded by S2, which causes low cell forwarding efficiency of S2; in addition, during the waiting time of the cell C2, the FIC in the LCC B keeps sending new cells, which causes cell accumulation in L2.